1. The Field of the Invention
The present invention relates to data storage on rotating magnetic storage devices. More particularly, the present invention relates to using micropositioners for positioning recording heads of a disk drive to create servo data on a disk for use in tracking during operation of the disk drive.
2. Background and Related Art
Hard disk drives are an important data storage medium for computers and other data processing systems. Magnetic hard disk drives have significantly improved in size, performance and cost due to many technology innovations. The prevalent trend in hard disk design is to make smaller hard disks with increasing track density, which is increasing demands in the servo control, i.e., accurate locating and following of tracks that hold the data.
FIG. 1 illustrates a conventional hard disk drive 100, which includes a single disk 120 and a single head gimble assembly (HGA) 140 with a macroactuator 160 and a slider, or recording head 180. In operation, a transducer positioned on the recording head 180 reads data that is magnetically encoded on the surface of the disk 120 or writes data to the surface of the disk 120. In order to access the appropriate sectors on the disk 120, the macroactuator 160 uses a closed-loop feedback or servo process to detect the position of the recording head 180 and adjust the position as needed.
Most conventional disk drives 100 have multiple recording heads 180 and can include multiple disks 120 in a disk stack. Most conventional hard drives 100, however, read and write data using one recording head 180 at a time, on various surfaces within the disk stack, rather than using multiple recording heads simultaneously, due to several physical limitations. The inability to use more than one recording head 180 at a time is a factor that has significantly limited improvements in the data rates of disk drives.
FIG. 2 illustrates a disk drive 200 with a disk stack that includes two disk platters 270a, 270b. Each disk 270a, 270b includes multiple tracks 210a, 210b, which are concentric sets of magnetic bits on the disk. Each track 210a, 210b is divided into sectors 210c, which are typically marked with an identification number within a sector header and are usually 512 bytes in size. A group of tracks having the same radius, such as tracks 210a and 210b, make up a cylinder within the disk drive. Tracks 210a and 210b can also be located on opposing surfaces of disk platters 270a and 270b. Accordingly, disk drive 200 has sliders or recording heads 220a, 220b, 220c, 220d on both sides of the disks 270a and 270b. 
Sliders 220a, 220b, 220c, 220d are attached to arms 260a, 260b, 260c, 260d, respectively, which are rotated by course actuator, or macroactuator, 240 about an axis of rotation 280. Typically, actuator 240 is a voice coil actuator that utilizes a closed-loop feedback system (i.e., servo system) to dynamically position the heads 220a, 220b, 220c, 220d directly over the data tracks 210a and 210b on both sides of disks 270a and 270b. Feedback is provided by data bits known as servo wedges 250 that are located between sectors of various tracks 210a, 210b. When in operation, spindle 230 of disk drive 200 rotates disks 270a, 270b while macroactuator 240 moves heads 220a, 220b, 220c, 220d in a radial direction to find the appropriate track 210a, 210b at which the desired data is stored.
The hard disk drive (HDD) servo system consists essentially of two modes of operation namely, the track seeking mode and the track following mode. The track seeking mode moves the heads 220a, 220b, 220c, 220d in the radial direction from a present track to a specific destination track in a minimum time using bounded control effort. The track-following mode is to control and keep the head in the correct position in the presence of noise and other disturbances while information is being read from or written to the hard disks 270a, 270b. 
FIG. 3 illustrates a magnified view of servo bit data used in assisting an actuator to keep the heads on track. As shown, data track 300 includes servo half bits 350 within a servo area 315 that is between data 305 within the track. Gray code and timing bits 320 are located just below the servo area 315, and a read-write transition 310 is located right after the servo area 315. A read head 325 is positioned into the center of the track and used as feedback to the servo system for adjusting an actuator arm as the heads move off-line. This is done through a measurement in comparison of the half bits 350 using a position error signal. Also shown in FIG. 3, when the heads are on track 330, the magnitude of the half bits on the “A” side of track 300 are equal in magnitude, within a predefined tolerance, of the half bits located on the opposite “B” side of track 300. As the head moves off-track 335, the magnitude of one side of the half bits falls below a predetermined threshold of the position error signal, and the appropriate feedback is provided to reposition the heads using the actuator arm.
To read and write data, the disk drive head must remain accurately centered on a selected track. Due to the increasing demand of higher track densities, the heads are being required to be centered on the narrow tracks within high tolerances of approximately one-millionth of an inch or less. Accordingly, the precision in writing servo data within a track is also increasing in complexity.
The process by which the tightly packaged magnetic servo bits are written onto the platter is referred to as servo writing. One conventional method for performing servo writing uses a high precision servo writing machine during the manufacturing of the device. The servo writing machine is an expensive device that is used to control the actuator during this process, as the servo writing progresses across the disk. Because the head stack is exposed through an opening in the drive, servo writing must also be done in a clean room environment with external sensors invading the head disk assembly to provide the precise angular and radial position information to write the servo patterns. Off-set servo wedges, as shown in FIG. 3, are formed in the drive by positioning the writer at half track during multiple revolutions, which requires each disk drive to be processed by the servo writing machine for a significant amount of time.
A second conventional alternative is to pre-write the servo track at the media level, prior to assembly into the drive. Issues with this approach, however, include the high capital costs of media level servo writers and the stacking tolerances during the drive assembly for multiple disk drives that require modifications to be made to the current drive architecture. In addition, neither type of the foregoing servo writing methods compensates for dynamic mechanical conditions in disk drives or in dedicated spinstands for single disk writing, such as thermal motion, drive induced vibration, spindle bearing runout, disk vibration/flutter, actuator windage, etc.